Membrane oxygenators for blood are attracting growing medical interest because of their capability of partially or completely taking over the respiratory function of a patient for a period of many hours and even days without unacceptable damage to the blood supply. Previously, bubble-type oxygenators involving the direct application of oxygen bubbles through a stream of blood had been used in open heart surgery for periods up to four or five hours. However, unacceptable damage frequently is inflicted upon the blood supply of the patient if the bubble oxygenators remain in operation for periods significantly longer than this.
Commercially available disposable membrane oxygenator units are disclosed in U.S. Pat. No. 3,757,955. The same patent describes a membrane oxygenator unit currently under development in which the membrane is made of a porous, hydrophobic material such as 3 or 4 mil polytetrafluoroethylene sheeting having an effective pore diameter of about 0.5 micron. Such materials are capable of rapidly transferring oxygen, carbon dioxide and water vapor, while preventing the transfer of blood itself through the membrane. Porous membrane oxygenator units exhibit an oxygen and carbon dioxide transfer capability which greatly exceeds the older membrane oxygenator unit designs which utilize thin silicone rubber membrane and the like. Accordingly, porous membrane oxygenator units can support the total respiratory needs of a patient with a significantly smaller total surface area of membrane than a conventional silicone rubber membrane oxygenator unit of similar design. As a result of this, the amount of blood which is removed from the body at any one time can be typically less with porous membrane oxygenator units, which is a significant and important advantage.
There is, however, a drawback to porous membrane oxygenator units: it is absolutely necessary for the pressure on the blood side of the membrane to at all times equal or exceed the pressure on the gas side of the membrane. If these conditions fail, the increased gas pressure may drive gas bubbles through the membrane into the blood flow path, from where the gas bubbles may be conveyed back to the patient. This could create a life-threatening embolism in the patient.
Accordingly, in U.S. patent application Ser. No. 390,567 filed Aug. 22, 1973 by Ronald J. Leonard, an oxygenator apparatus is provided for the safe and effective utilization of hydrophobic, porous membrane blood oxygenator units. In the device described in the patent application, a manometer means is provided to assure safe and reliable limitation of the gas pressure in the oxygenator unit.
Also, the aforesaid application discloses heat exchanging means and the like for maintaining the appropriate blood temperature and other desirable parameters of operation.
For the commercial manufacturer of porous membrane blood oxygenator units, it is a matter of great importance to be certain that the customers utilize the oxygenator unit in a correct manner, using the correct equipment for mounting and supplying blood and oxygen to the membrane oxygenator unit, so that there will be no dangerous gas overpressure, driving oxygen bubbles into the blood path, which can instantly create a life-threatening situation.
In accordance with this invention, an oxygenator and membrane oxygenator unit for use therein are provided in which the membrane oxygenator unit is used only with great difficultly apart from the oxygenator itself, which can be designed to provide the necessary parameters of operation that result in safe use. Accordingly, a relative foolproof system is provided for the protection of patients.
Furthermore, in accordance with this invention, a system is provided for assured, unrestricted exhaust of gas, to prevent any obstruction of the flow of gas from the oxygenator unit, thus avoiding a consequent, potentially disastrous rise in the gas pressure of the oxygen flow path in the oxygenator unit.